2004 5.7L LS1 GTO Specific Wiring Harness information.   This year GTO used cable throttle.

2004 5.7L LS1 GTO Wiring Schematics

2004 5.7L LS1 GTO PCM Pinouts – Includes highlighted pins for removal, and those to keep for external connections. PDF FILE

2004 5.7L LS1 GTO Harness Pictures – I’ve got some modified wiring harness pictures some place, will get them added when I find them.